AIM:To observe the biotransformation process of a Chinese compound,aesculin,by human gut bacteria,and to identify its metabolites in rat urine.METHODS:Representative human gut bacteria were collected from 20 healthy volunteers,and then utilized in vitro to biotransform aesculin under anaerobic conditions.At 0,2,4,8,12,16,24,48 and 72 h post- incubation,10 mL of culture medium was collected.Metabolites of aesculin were extracted 3×from rat urine with methanol and analyzed by HPLC.For in vivo metabolite analysis,aesculetin(100 mg/kg)was administered to rats via stomach gavage,rat urine was collected from 6 to 48 h post-administration,and metabolite analysis was performed by LC/ESI-MS and MS/MS in the positive and negative modes.RESULTS:Human gut bacteria could completely convert aesculin into aesculetin in vitro.The biotransformation process occurred from 8 to 24 h post-incubation,with its highest activity was seen from 8 to 12 h.The in vitro process was much slower than the in vivo process.In contrast to the in vitro model,six aesculetin metabolites were identified in rat urine,including 6-hydroxy-7-gluco- coumarin(M1),6-hydroxy-7-sulf-coumarin(M2),6,7-di- gluco-coumarin(M3),6-glc-7-gluco-coumarin(M4),6-O-methyl-7-gluco-coumarin(M5)and 6-O-methyl-7- sulf-coumarin(M6).Of which,M2 and M6 were novel metabolites.CONCLUSION:Aesculin can be transferred into aesculetin by human gut bacteria and is further modified by the host in vivo.The diverse metabolites of aesculin may explain its pleiotropic pharmaceutical effects. AIM: To observe the biotransformation process of a Chinese compound, aesculin, by human gut bacteria, and to identify its metabolites in rat urine.METHODS:Representative human gut bacteria were collected from 20 healthy volunteers, and then laid out in vitro to biotransform aesculin under Anaerobic conditions.At 0,2,4,8,12,16,24,48 and 72 h post- incubation,10 mL of culture medium was collected.Metabolites of aesculin were extracted 3×from rat urine with methanol and analyzed by HPLC .For in vivo metabolite analysis,aesculetin(100 mg/kg)was administered to rats via stomach gavage,rat urine was collected from 6 to 48 h post-administration, and metabolite analysis was performed by LC/ESI-MS and MS/MS In the positive and negative modes.RESULTS:Human gut bacteria could completely convert aesculin into aesculetin in vitro.The biotransformation process occurred from 8 to 24 h post-incubation, with its highest activity was seen from 8 to 12 h.The in vitro process Was much slower than the in vivo pro cess.In contrast to the in vitro model, six aesculetin metabolites were identified in rat urine, including 6-hydroxy-7-gluco- coumarin(M1),6-hydroxy-7-sulf-coumarin(M2),6,7- Di-gluco-coumarin(M3),6-glc-7-gluco-coumarin(M4),6-O-methyl-7-gluco-coumarin(M5)and 6-O-methyl-7-sulf-coumarin(M6 ).Of which, M2 and M6 were novel metabolites.CONCLUSION:Aesculin can be transferred into aesculetin by human gut bacteria and is further modified by the host in vivo.The diverse metabolites of aesculin may explain its pleiotropic pharmaceutical effects.